214 REPORT—1883. 
capable of producing in bodies on the earth’s surface. One estimate of 
these stresses is the acceleration a body receives. 
2 
Intensity thus defined may be written ses where V is the maximum 
velocity of a vibrating particle, and @ is its amplitude, or half a semi- 
oscillation. This quantity, ie is the maximum acceleration of an earth- 
particle, assuming the motion to be simple harmonic. 
I have calculated v for the prominent vibrations of a number of 
disturbances, each disturbance being recorded at several stations. 
The results of these calculations show that as a disturbance radiates the 
intensity dies out, rapidly at first, but eventually very slowly. The results 
give a curve which is a rough approximation to an equilateral hyperbola. 
Hrom these observations it would appear that by obtaining the curve 
of intensity for any given disturbance we may, by comparing with the 
curves obtained by the explosion of known charges of dynamite, approxi- 
mately obtain some absolute measures of earthquake energy. 
The accompanying diagram gives the mean of the results ohtained in 
a series of experiments in whick the surface of the ground was put into 
vibration by the explosion of charges of dynamite put into bore-holes 
about ten feet deep. The ordinates give intensity, and the abscissxe 
distance from the origin in feet. 
metres per second, 
Mean acceleration in thousands of mllli- 
Origin 100! 200! 300! 400/ 
Scale in feet 
Curve of Earthquake Intensity. 
The shocks which are usually felt in Tokio and Yokohama, as 
calculated from diagrams, have a maximum acceleration of from 20 to 
200 millimétres per second. When this exceeds 300 millimétres we may 
expect chimneys to be cracked, and slight damage of alike nature done 
to buildings. 
To complete this investigation I have the intention of comparing 
together the maximum velocity of an earth-particle, as computed from a 
diagram, with that calculated by the projection or overthrow of a body 
of known dimension—the impulse being given by the explosion of a 
charge of dynamite. 
An investigation which I described in my last report to the British 
Association was the determination of the existence of an earth-current at 
the time of an earthquake. I then stated that a strong current was 
produced in a land line connected with an earth plate which had been 
shaken. This confirmed the numerous records which we have of currents 
